For perhaps the first time since being sworn into office, President Obama has articulated, in eloquent terms, what it means to be a progressive. In his budget speech last week, he spoke of our obligation to the broader community to provide a basic level of security and dignity. Speaking of programs such as Medicare, Medicaid and Social Security, he said what every good progressive believes: “We would not be a great country without those commitments.”

He fused a defense of progressive governance with a scathing critique of Paul Ryan’s cruel budget, which all but four Republican House members have now voted for. And he demanded that the rich finally pay their fair share, vowing to let the Bush tax cuts expire. It was a powerful speech, in many ways reassuring to progressives who have been demoralized by a president who appeared missing in action.

But rhetoric and policy are not the same thing. And in this case, as in far too many, the policy agenda the president has laid out is not worthy of, in his words, “the America we believe in.”

To begin with, the president continues to let Republicans define the playing field in almost every instance. Why is the debate we are having not about whether to cut, but how much to cut? Why isn’t it about the urgency of joblessness instead of the perils of deficits? The budget the president proposed is clearly influenced by a discredited conservative economic worldview. It shouldn’t be accepted as the “progressive” alternative in the negotiations soon to come.

What’s worse is that, even on this narrow playing field, the president isn’t fighting harder for those who need government’s support the most. He has jettisoned the Keynesian thinking this era demands, prematurely embracing what might be described an austerity-lite policy, one that all but guarantees mass unemployment as the new normal.

In his speech, he spoke eloquently of how there was “nothing courageous about asking for sacrifice from those who can least afford it and don’t have any clout on Capitol Hill.” Nothing courageous, indeed. And yet it is President Obama who has said that for every $1 in tax increases, we should create $2 in spending cuts. Faced with the choice between new cuts to the social safety net and new taxes for the richest few, it is not just Paul Ryan but President Obama whose acceptance of the way this choice is framed leaves the poor shouldering most of the burden.

The most progressive president since Lyndon Johnson should be willing to embrace a bolder opening gambit. He should not be so willing to compromise on principle, even when ultimate compromise may be necessary. Real leadership might require compromise, but it cannot be defined by compromise. It must instead be defined by a clear vision for the future, and most important, a willingness to defend it. It should be focused not on what is possible, but instead, on the most that is possible; not the path of least resistance, but the path of maximum potential benefit.

Failing to do so is what can produce a Tea Party budget, such as the one adopted last week. As Paul Krugman put it in his column this week, the two parties “don’t just live in different moral universes, they also live in different intellectual universes.” Any embrace or acceptance of that Republican universe by the White House is a retreat from the reforms this country desperately needs — and was promised.

Yet the president has again telegraphed his willingness to compromise, admitting in his speech that he did not “expect the details in any final agreement to look exactly like the approach” he laid out. What, then, does he expect it will look like?

The further right this process moves — whether as a result of a political system warped and broken by corporate interests protecting their privilege, or lobbyists actively gutting reform — the more disheartening the definition of victory becomes. Is merely preventing Republicans from ending Medicare what victory looks like now? Yes, we need a defensive opposition, but while Democrats control the Senate and the White House, they cannot act merely as a minority party. Shouldn’t they be laying out a clear vision of a sustainable and fair economy? As the extremists take over the GOP, is the Democratic Party really going to be content to define success so modestly?

There are at least 83 Democratic members of the House who believe that we cannot exclude alternatives that would solve this economic challenge more justly and fairly. They believe we must challenge the limits of our narrowing debate and expand, as President Obama once called it, “our moral imagination.”

They are the members of the Congressional Progressive Caucus (CPC), who last week introduced what they are calling the “People’s Budget,” an alternative both to President Obama’s proposal and the unconscionable Ryan Budget.

It lays out what a robust progressive agenda should look like. It protects the social safety net, promotes a progressive tax policy and makes significant cuts to the Pentagon by bringing our troops home from Iraq and Afghanistan. It actually generates a surplus by 2021, according to Rep. Raul Grijalva, co-chair of the CPC.

This is the kind of budget our president should be proposing. This is the kind of budget the progressive community should be rallying around. One that makes millionaires, billionaires and corporations pay their fair share. One that protects the poor and middle class. But it is the kind of budget that establishment Democrats and media elites are inclined to ignore and dismiss.

We can be, as Nobel Prize-winning economist Joseph Stiglitz recently put it, a country “of the 1%, for the 1%, by the 1%.” Or we can be a country that believes in — and embraces — shared sacrifice. A country not defined by the greed of the few but by the needs of the many.

That’s the only kind of America really worth believing in.

Katrina vanden Heuvel is editor and publisher of The Nation. She writes a weekly online column for The Post.